This project will evaluate physiologic and psychophysiologic effects of respirator use to develop adequate guidelines for medical certification programs and to facilitate design of better tolerated (and hence more effectively used) respirators. Much previous work has focused upon their effects on maximal work ability and on the ability of an individual to overcome the effects of dead space, resistance, and thermal loads. This project will examine the hypothesis that in most normal and moderately impaired persons, the ability to use a respirator is not determined by these factors, but rather is determined by the adaptation of an appropriate respiratory pattern and by psychophysiologic sensitivity to respiratory loads. Three types of studies will be performed: l. EXERCISE LABORATORY STUDIES will measure "mechanical" factors (flows, pressures), respiratory timing and pattern, load sensitivity, and metabolic (e.g., oxygen and carbon dioxide volumes) variables in normal and impaired subjects. Measurements will be made at three pseudosteady state exercise levels followed by a ramp period of rapidly increasing exercise in order to identify the factors which critically limit respirator use. Artefact caused by mouthpiece use in previous studies will be estimated. 2. AMBULATORY STUDIES will measure flows, volumes, and respiratory timing and pattern variables under field conditions. 3. DETERMINANTS OF TOLERANCE STUDIES will test load sensitivity, respiratory pattern, and respirator tolerance in a large sample to help define normal variability. Respiratory timing and pattern measurements will employ a modified respiratory inductance plethysmograph system. It will be done with an FM tape recorder to allow off-line processing and ambulatory use. Load sensitivity will be measured using the "Psychophysical Law", in which perception (P) and Resistance (R) are related: P Alpha R exp(n), "n" representing an individual's sensitivity. These studies should define the normal response, characterize responses in impaired persons, and determine if tolerance depends primarily on factors other than simple muscle ability to overcome respirator loads.